The present invention generally relates to a pattern display signal generating apparatus, and in particular to a pattern display signal generating apparatus capable of generating a pattern display signal which enables a pattern to be displayed so that a contour of the character pattern is highlighted. The present invention further relates to a pattern display apparatus using the present pattern display signal generating apparatus.
Conventionally, various display formats are used for producing a visual image of patterns of characters figures on a picture plane, of a display unit such as television sets. A highlighting display of characters is one example of the display formats. For example, when highlighting the display of characters such as letters, numerals and symbols, the entire character is highly and uniformly intensified, or only a contour of the character is highly brightened. In the latter highlighting display, the contour of the character is visually emphasized compared to other portions thereof and is displayed.
A display apparatus comprises a pattern display signal generating apparatus for generating a pattern display signal. The pattern display signal generating apparatus includes a character generator capable of generating dot patterns of characters. One dot pattern is arranged in a dot matrix of N lines and M columns. A dot pattern signal corresponding to one character is read cut from the character generator line by line, and is supplied as a pattern display signal to a signal processing circuit. The signal processing circuit generates a video signal from the pattern display signal. The video signal is supplied to a display unit such as a cathode ray tube display unit, and the corresponding character is displayed on a display picture plane thereof.
The conventional pattern display signal generating apparatus further includes an operation circuit for generating a specific pattern display signal which enables the highlighting display of the contour of the character (hereafter referred to as a contour highlighting display signal). The operation circuit generates the contour highlighting display signal corresponding to a dot pattern of only the contour of the character by using the dot pattern signal read out from the character generator. In this case, the contour of the dot pattern has a width of one dot in a direction of lines in the pattern (raster scan direction), for example.
The contour highlighting display signal for forming the contour pattern having the width of one dot is generated by subjecting all the dots of an N x M dot matrix to the following processing. Referring to FIG. 1 which shows a portion of the N.times.M dot matrix, when a dot positioned at the n'th line and the m'th column (hereafter represented as (n, m)) is processed, data, of its neighboring dots, i.e., 8 dots represented by the shaded squares, are read out from the character generator in addition to the datum of the dot at the position (n, m). The operation circuit built into the pattern display signal generating apparatus performs a predetermined operation on the 9 dot data, and decides whether or not the dot at the position (n, m) is necessary to form the dot pattern of the contour. If the result of the operation is affirmative, the dot subjected to the operation is decided to be a dot forming the contour.
However, the above-mentioned process for obtaining the dot pattern of the contour is very complex. In addition, the operation circuit which is designed specifically for implementing the aforementioned process cannot generate a different contour dot pattern having a width amounting to two dots in the direction of the line for example. From this reason, a degree of flexibility in the display format of the highlighting contour is poor.
In order to eliminate the above problems, a display pattern signal generating apparatus having a configuration shown in FIG. 2 is proposed. Referring to FIG. 2, a memory 10 stores dot pattern data of various characters, and a memory 11 stores a dot pattern of a center or inner) region of each character obtained by removing a dot pattern of a contour thereof.
Data which is simultaneously read out from the memory 10 and 11 in response to the same address signal ADDS is subjected to parallel-to-serial conversion in shift registers 12 and 13, respectively. The conversion is performed in synchronization with a clock signal .phi. supplied to the shift registers 12 and 13. The shift registers 12 and 13 output serial signals to output terminals 14 and 15 of the pattern display signal generating apparatus, respectively. At the same time, the outputs of the shift registers 12 and 13 are supplied to an exclusive-OR circuit 16. A result of the exclusive-OR operation is a contour highlighting display signal related to the dot corresponding to the address ADDS. The contour highlighting display signal is supplied to an output terminal 17. In this manner, the contour highlighting display signal related to all the N.times.M dots is generated.
However, the configuration shown in FIG. 2 must store two dot patterns associated with one character, and thus a large memory capacity is necessary.